Williams Hazens Equation of Head Loss

The Williams Hazen equation can be used to calculate head loss in pipes or tubes due to friction

The Williams Hazen formula for calculating head loss in pipes and tubes due to friction can be expressed as:

h_l = 0.002083 l (100 / c)^1.85 (q)^1.85/ (d_h)^4.8655 (1)

where

h_l = head loss (ft)

l = pipe or tube length (ft)

c = design coefficient determined for the type of pipe or tube

q = flow rate (gal/min)

d_h = hydraulic diameter (inch)

Note! The Hazen Williams formula gives accurate head loss due to friction for fluids with kinematic viscosity of approximately 1.1 cSt. More about kinematic viscosity for several fluids.

The results form the formula is acceptable for cold water at 60 ^oF (15.6 ^oC) with kinematic viscosity 1.13 cSt. For hot water with a lower kinematic viscosity (0.55 cSt at 130 ^oF (54.4 ^oC)) the error will be significant.

Since the Hazen Williams method is only valid for water flowing at ordinary temperatures between 40 to 75 ^oF, the Darcy Weisbach method should be used for other liquids or gases.

The Design Factor - c

The design factor is determined for the type of pipe or tube used:

• The c-value for cast iron and wrought iron pipes or tubes ranges from 80 to 150, with average value 130 and design value 100.
• The c-value for copper, glass or brass pipes or tubes ranges from 120 to 150, with average value 140 and design value 140.
• The c-value for cement lined steel or iron pipes has average value of 150 and design value 140.
• The c-value for epoxy, vinyl ester and isopphthalic pipes can be set to 150.

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